The present invention relates to a radiation image erase unit, and more particularly to a radiation image erase unit for erasing remaining radiation image from a stimulable phosphor sheet by exposing the stimulable phosphor sheet to erasing light emitted from an erase light source housed in the casing of the image erase unit, the radiation image erase unit being arranged to prevent the erasing light from heating at least a portion of the wall of the casing and also to prevent the stimulable phosphor sheet in an image-erasable condition from being damaged by heat radiation from the casing wall.
There has in recent years been proposed a radiation image recording and reproducing system in which a radiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor is a phosphor which, when exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode ray, or ultraviolet rays, stores a part of the energy of the radiation. When the stimulable phosphor exposed to the radiation is subsequently exposed to stimulating light such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation.
The radiation image recording and reproducing system employs such a stimulable phosphor. More specifically, the radiation image of an object such as a human body is stored in a sheet having a layer of stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a "phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating light such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic film material or on a display unit such as a cathode ray tube (CRT).
The aforesaid radiation image recording and reproducing system is disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Laid-Open Patent Publication. No. 56-11395, for example.
The radiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of radiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation to which the stimulable phosphor is exposed varies widely under various conditions, radiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric conversion means for detecting and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photosensitive material or on a display unit such as a CRT.
The radiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the radiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly or recyclically, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the remaining radiation energy on the stimulable phosphor sheet after the radiation image has been read out by stimulating light is discharged by exposure to light, and the stimulable phosphor sheet is employed again for recording a radiation image thereon. The erasure of the radiation energy from the stimulable phosphor sheet is disclosed in U.S. Pat. No. 4,400,619, for example.
An image erase mechanism for removing the remaining radiation image from the stimulable phosphor sheet after the desired image has been read therefrom should preferably be assembled as a unit in the radiation image read-out apparatus. To allow the image erase mechanism to be easily assembled in the apparatus, the overall apparatus is required to be compact and so is the image erase mechanism. The applicant has already proposed a box-shaped image erase unit as a compact image erase mechanism for use with stimulable phosphor sheets, the image erase unit comprising a casing accommodating erase light sources and a feed means disposed within or without the casing for delivering stimulable phosphor sheets to a desired position (see Japanese Patent Application Nos. 59-112532, 59-112533, and 59-112534).
In the box-type image erase mechanism which is required to be compact in size, the erase light sources and the wall of the casing are disposed quite closely to each other. As a result, the casing wall is heated by the heat radiated from the erase light sources to adversely affect the stimulable phosphor sheet in the casing. The erase light sources are capable of irradiating the stimulable phosphor sheet with a high illuminance for substantially thoroughly discharging any remaining radiation energy from the sheet. In order to erase the remaining image completely and in a short time from the phosphor sheet with the erasure light, an increased number of erase light sources and an increased amount of erasure light should be employed to generate intensive erasure light. The increased number of erase light sources and the increased amount of erasure light, however, tend to heat the image erase mechansim excessively, resulting in damage to the image erase mechanism, the sheet, and the surrounding components.
As disclosed in Japanese Laid-Open Patent Publication No. 55-146447, the stimulable phosphor sheet comprises a support made of paper or a high polymeric organic material such as polyethylene terephthalate, and a phosphor layer deposited on the support. The phosphor layer is composed of a binder made of high polymeric organic material such as nitrocellulose, and stimulable phosphor particles dispersed in the binder. A transparent protective layer is deposited on the surface of the phosphor layer which is opposite to the support for physically or chemically protecting the phosphor layer. The protective layer is also made of a high polymeric organic matcrial such as polyethylene terephthalate. Since the stimulable phosphor sheet is composed of organic materials that are easily susceptible to thermally induced deformation and/or property modification, the stimulable phosphor sheet, when subjected to excess heat from the erase light sources or the casing wall heated by the erase light sources, is apt to be deformed and/or modified. Thus, the sheet may not be reused smoothly, or cannot entirely be reused.
The casing of the box-type image erase mechanism is substantially fully closed except for inlet and outlet openings for stimulable phosphor sheets. Therefore, the wall of the casing is unduly heated by erasure light, except where the inner casing wall surface has a mirror finish for effectively reflecting the erasure light to the stimulable phosphor sheet in the casing. The heat radiation from the casing wall is highly likely to heat and damage the stimulable phosphor sheet. The casing wall is heated directly by the erasure light especially when there is no stimulable phosphor sheet present in the casing.